This invention relates to cardiac monitors, and more particularly to a system for simultaneous arrhythmia monitoring and ECG analysis on a real time basis.
Electrocardiographs for acquiring and analyzing multiple leads of conventional ECG are known. For example, electrocardiographs manufactured by Marquette Electronics, Inc. of Milwaukee, Wis., include a twelve lead software program called the 12SL ECG Analysis Program. Eight of the leads (I, II, V1-V6) are acquired directly and the remaining four (III, aVR, aVL and aVF) are derived using Einthoven's Law. Each lead of ECG can be considered a view of the heart from a different angle. The program also determines the origin of the predominate rhythm from major categories such as electronic artificial pacing, atrial flutter, ectopic atrial rhythm, sinus rhythm, junction rhythm and atrial fibrillation. In addition, the program analyzes the contour of the QRS waveform using conventional criteria for Wollf-Parkinson-White atrial hypertrophy, QRS abnormalities, ST abnormalities-QRS related, ST elevation abnormalities, ST depression abnormalities and T wave abnormalities. These allow the physician to determine the existence of rhythm abnormalities, conduction abnormalities, hypertrophy, infarction and repolarization. This prior art program acquires ECG data for non real time or delayed analysis.
Cardiac monitors are also well-known for analyzing cardiac arrhythmia or beat irregularities. One such system is the EK-Pro arrhythmia analysis algorithm sold by Marquette Electronics, Inc. of Milwaukee, Wis. This system analyzes four ECG leads (I, II, III and V1) to determine the occurrence of such conditions as ventricular asystole, ventricular fibrillation, ventricular tachycardia, VT3-5, R-on-T, ventricular bradycardia, couplet, bigeminy, accelerated ventricular rhythm, pause, trigeminy, premature ventricular complexes, ST deviation, tachycardia, bradycardia, and irregular beats.
Arrhythmia monitors are generally rhythm sensing systems which can indicate the occurrence of and classify arrhythmias on a real time basis, but do not indicate their cause. ECG lead analyzers, on the other hand, can determine the condition of the entire myocardium. Present practice is to employ an arrhythmia monitor for triggering an alarm upon the occurrence of an arrhythmia. The patient will then be connected to an electrocardiograph in an attempt to determine its cause. However, in certain situations, such as upon the occurrence of an acute infarction, the patient is at highest risk during the initial stages of the infarct when an area of the myocardium is jeopardized due to ischemia but before the myocardium is damaged. This condition directly leads to a high probability of ventricular arrhythmia during the time when the patient's heart is already suffering from a lack of oxygenated blood. However, such an ischemic episode will not be detected by an arrhythmia monitor prior to the occurrence of ventricular arrhythmia.